Velocity v = Volumetric flow ...

Velocity v = Volumetric flow rate Q ÷ pipe cross-sectional area A. For the pressure, calculate your total head loss & required delivery pressure. Once you have these two you can check the pump curve to size the pump. Normal practice is to chose the nearest larger size pipe diameter to reduce head loss. This is especially applicable if v = 0.6m/s is the maximum velocity your client will accept. If it's the minimum velocity then choose the next smaller pipe size, but ensure your head loss is acceptable